In 1955, he received a BA in Chinese Literature from the University of Tokyo, and began graduate studies, but dropped out of the doctoral course in 1960.

Mantarō Hashimoto was married to Anne Oi-kan Yue-Hashimoto, who is currently Professor Emeritus of Chinese Language and Linguistics at the University of Washington.

According to one prominent linguist of Chinese, Hashimoto blazed the trail for two fields of research: the effect that geography has on historical linguistics, and how areal features in the varieties of Chinese (previously called "dialects") reflect prolonged language contact with other language families (Wang 1987: 378).

Professor Hashimoto was a leading advocate of studying different areal features to gain information on the historical development of the Chinese language.

The polyglot Mantarō Hashimoto was a prolific writer of scholarly publications in Japanese, English, and Chinese (see Tsuji 1988 for details).